The present application claims priority to Japanese Application No. P10-274983 filed Sep. 29, 1998 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a memory device for storing information by accumulating electrical charges moved from a conduction region for memory in a storage region and a manufacturing method thereof, and an integrated circuit thereof for integrating such memory devices. More specifically, the present invention relates to a memory device having the conduction region for memory formed on an insulator and a manufacturing method thereof, and an integrated circuit thereof for integrating such memory devices.
2. Description of the Related Art
A typical memory device according to the related art, EEPROM (Electrically Erasable Programmable Read-Only Memory) or flash memory, for instance, is provided with a layer of storage region between a memory gate electrode and a conduction region. The storage region stores information by accumulating electrical charges (that is, electrons or holes) moved from the conduction region to this storage region by tunnel effects. The insulating film between the conduction region and the storage region has been formed hitherto by thermal-oxidation of the surface of the conduction region made of silicon (Si) at a high temperature in the range of 800-1000xc2x0 C.
As described above, in the memory device according to the related art, the insulating film has been formed by heat treatment at a high temperature. As a result, the memory device is unable to be formed on a substrate made of insulator such as silicate glass, quartz glass or plastics, which have a low melting point.
On the other hand, if we try to form the insulating film by thermal oxidation at a low temperature of 500xc2x0 C. or lower, high insulation performance cannot be achieved. In addition, electrical charges accumulated in the storage region leak to the conduction region in a short time through a large amount of defects in the insulating film, and thus the information is unable to be stored over a long period of time.
It is therefore an object of the present invention to provide a memory device which can store information over a long period of time even when it is manufactured at low temperatures and a manufacturing method thereof, and an integrated circuit for integrating such memory devices.
A memory device according to the present invention comprises: a base portion made of an insulator; a conduction region for memory made of a semiconductor provided on one surface of the base portion; a first impurity region provided adjacent to the conduction region for memory; a second impurity region separated from the first impurity region and provided adjacent to this conduction region for memory; a storage region comprising a plurality of dispersed particulates for accumulating electrical charges moved from the conduction region for memory; a tunnel insulating film provided between the storage region and the conduction region for memory; a control electrode for memory for controlling the electrical charge amount of the storage region and the conductivity of the conduction region for memory; an insulating film for controlling memory provided between the control electrode for memory and the storage region; a conduction region for selection provided on part of the base portion, which is adjacent to the second impurity region and separated from the conduction region for memory; a third impurity region provided adjacent to the conduction region for selection and separated from the second impurity region; a control electrode for selection for controlling the conductivity of the conduction region for selection; and an insulating film for controlling selection provided between the control electrode for selection and the conduction region for selection.
A method for manufacturing a memory device according to the present invention comprises the steps of: forming a conduction region for memory and a conduction region for selection made of semiconductors on a base portion made of an insulator; forming a tunnel insulating film on the conduction region for memory; forming a storage region comprising a plurality of particulates dispersed on the tunnel insulating film; forming an insulating film for controlling memory on the storage region while forming an insulating film for controlling selection on the conduction region for selection; forming a control electrode for memory on the insulating film for controlling memory while forming a control electrode for selection on the insulating film for controlling selection; and forming a first impurity region adjacent to the conduction region for memory, a second impurity region separated from the first impurity region and adjacent to the conduction region for memory and to the conduction region for selection, and a third impurity region separated from the second impurity region and adjacent to the conduction region for selection.
An integrated circuit according to the present invention has a plurality of memory devices integrated, and each of the memory devices comprises a base portion made of an insulator, a conduction region for memory made of a semiconductor provided on one surface of the base portion, a first impurity region provided adjacent to the conduction region for memory, a second impurity region separated from the first impurity region and provided adjacent to the conduction region for memory, a storage region comprising a plurality of dispersed particulates for accumulating electrical charges moved from the conduction region for memory, a tunnel insulating film provided between the storage region and the conduction region for memory, a control electrode for memory for controlling the electrical charge amount of the storage region and the conductivity of the conduction region for memory, an insulating film for controlling memory provided between the control electrode for memory and the storage region, a conduction region for selection provided on one surface of the base portion, which is adjacent to the second impurity region and separated from the conduction region for memory, a third impurity region provided adjacent to the conduction region for selection and separated from the second impurity region, a control electrode for selection for controlling the conductivity of the conduct ion region for selection; and an insulating film for controlling selection provided between the control electrode for selection and the conduction region for selection.
In the memory device according to the present invention, the conductivity of the conduction region for selection is controlled through applying voltage to the control electrode for selection, and accordingly, the conductivity of the conduction region for memory is controlled. In addition, electrical charges are moved from the conduction region for memory to the storage region to be accumulated in the storage region by applying voltage to the control electrode for memory, and the information is thereby written into the device. In the device, the storage region comprises plurality of dispersed particulates. Therefore, electrical charges accumulated in particulates formed at the non-defect region in the tunnel insulating film do not leak even if electrical charges accumulated in part of particulates leak through defects in the tunnel insulating film. Consequently, information can be stored over a long period of time.
In the method for manufacturing a memory device according to the present invention, first of all, a conduction region for memory and a conduction region for selection made of a semiconductor are formed on the base portion made of insulator. Then, on the conduction region for memory, a tunnel insulating film is formed, on which the storage region comprising the plurality of dispersed particulates is formed. Successively, on the storage region, an insulating film for controlling memory is formed, and the insulating film for controlling selection is formed on the conduction region for selection. Thereafter, on the insulating film for controlling memory, a control electrode for memory is formed, and on the insulating film for controlling selection, the control electrode for selection is formed. In addition, the first impurity region, the second impurity region, and the third impurity region are formed, respectively.
The integrated circuit according to the present invention has memory devices according to the present invention. Since the storage region is constructed with a plurality of dispersed particulates, the information can be stored over a long period of time.
Other and further objects, features and advantages of the invention will appear more fully from the following description.